The present invention relates to an electrophotographic copier, laser printer, facsimile apparatus or similar image recorder and, more particularly, to an image forming apparatus having an charging device provided at a constant distance from the surface of a photosensitive element. In an image forming apparatus which employs an eletrostatic photographic process, photosensitive element has its surface uniformly charged by a charging device, and electrostatic latent image is formed on the surface of the photosensitive element by an optical beam.
To charge the surface of the photosensitive element uniformly, the image forming apparatus must be arranged accurately to keep a constant distance between the surface of the photosensitive element and the charging device.
Particularly, in the case that the charging device is composed as a part of an integrated unit with another device, for example, a cleaning unit which is located around the surface of the photosensitive element, it is difficult to keep an accurate position of charging device against the surface of the photosensitive element.
According to the prior art, as the controlled method to have a constant distance between the surface of the photosensitive element and the charging device, there are some known methods; one method is that the charging device is fixed to the predetermined position after mounting on a main body frame, and the distance of the gap between the surface of the photosensitive element and the charging wire of the charging device is adjusted. Still another method is that a roller which is mounted on the charging device is in contact with the surface of the photosensitive element so that the wire of the charging device can be positioned at a constant distance with respect to the surface of the photosensitive element.
This typical known method is described in U.S. Pat. No. 4,627,701.
However, such method may incur many problems; it would take a long time to assemble the charging device and adjust the gap between the surface of the photosensitive element and the charging device, it would result in higher cost, the surface of the photosensitive element would be scratched by a service person during the above mentioned adjusting time.